Ultra-black Camouflage in Deep-Sea Fishes

Engineering flexible superblack materials

Flexible superblack materials are crucial for minimizing stray light, complicating object identification, and serving as low reflectance standards. However, the applications of existing superblack materials are limited due to challenges related to cost-effective scalable manufacturing, surface durability, and material conformability. Furthermore, existing fabrication platforms struggle to tailor superblack materials to application-specific needs. This work introduces an engineering platform that combines silicon mold fabrication and polymer casting to produce flexible superblack materials. This platform achieves repeatable wafer-scale production of superblack materials with a minimum reflectance of 0.15% and less than 0.4% across the visible spectrum. The sample reflectance is weakly dependent on illumination angles from 0° to 50° and observer angles from 0° to 70° when the illumination angle is less than 20°. This Lambertian-like reflectance profile enables the material to effectively conceal three-dimensional features in digital images even under intense lighting conditions. This platform can engineer the material surface to withstand tweezer scratches without significantly compromising its reflectance properties. This work introduces an engineering platform for designing flexible superblack materials, addressing key challenges in scalability, surface durability, mechanical flexibility, and customization.

Suspending Light-Absorbing Nanoparticles in Silica Aerogel Enables Numerous Superblacks

Current strategies for constructing sparse nanostructures for fabricating superblacks are only suitable for a few light-absorbing materials, severely limiting their applications. Herein, ultra-low reflective silica aerogels with ultra-high light transparency are used as solid smokes to individually or simultaneously suspend at least 100 species of light-absorbing nanoparticles with a volume fraction as low as 0.005%, for creating > 100 superblacks in practice and one billion superblacks in theory if taken permutation and combination among these 0D, 1D, or 2D nanoparticles into account. Depending on the composition of suspended nanoparticles and the structure of solid smoke, the resulting mechanically robust superblacks with supplementary properties including magnetism, full-spectrum absorption, high thermal stability, and excellent mechanical strength, are first observed. The wide choice of metallic or semiconductive LNs allows as-made superblacks to glitter in different catalytic reactions, and the resulting superblacks have been on-demand modified for endowing the self-cleaning performance in some contaminable environments. Benefiting from the superblack feature and porous network, these superblack monoliths have shown high-efficiency solar-heat conversion in some emerging light harvesting and managing fields. This powerful synthetic strategy for superblacks is expected to inspire researchers to conduct in-depth investigations on super-black optics, functional materials, etc.

Variation in lanternfish (Myctophidae) photophore structure: A comprehensive comparative analysis

The deep-sea open ocean habitat (below 200 m depth) is comprised of little-to-no light, near freezing temperatures, and vastly connected stratified waters. Bioluminescence is often linked to the success and diversification of fishes in these dark deep-sea habitats, which are host to many species-rich and morphologically diverse clades. Fish bioluminescence takes many forms and is used in a variety of behaviors including counterillumination, prey detection and luring, communication, and predator avoidance. This study focuses on lanternfishes (Myctophidae), a diverse group (252 spp. in 34 genera) of deep-sea fishes in which bioluminescence has played a critical role in their diversification. Using histological techniques, we provide new morphological analyses of the complex structure of the primary photophores of representative species from 17 genera in which photophore morphology has not previously been described. We combine this information with data from prior studies to compare primary photophore characteristics for species representing all 34 lanternfish genera. Although we find that lanternfish primary photophores are similar in many of their structural components, including the possession of a modified scale cup, photocytes, pigment, and reflector layers, we observe significant variation among species in other aspects of photophore morphology. Observed morphological differences include variation in pigmentation and in the calcification and thickness of the modified scale cup. We also find reflectors that are very thin or absent in gymnoscopeline and lampanyctine species, relative to the robust reflectors present in myctophine species. We find evidence of secondary reflectors and secondary pigment layers in six lanternfish species and observe major differences in scale-lens thickness and mineralization across the assemblage. Lastly, Scopelopsis multipunctatus is the only species analyzed lacking a photophore cup. Obtaining finer detail of light organ morphology across this species-rich lineage provides much-needed insight into the factors that have contributed to the remarkable diversity of lanternfishes in the deep open ocean.

Using high-resolution microscopy data to generate realistic structures for electromagnetic FDTD simulations from complex biological models

Finite-difference time-domain (FDTD) electromagnetic simulations are a computational method that has seen much success in the study of biological optics; however, such simulations are often hindered by the difficulty of faithfully replicating complex biological microstructures in the simulation space. Recently, we designed simulations to calculate the trajectory of electromagnetic light waves through realistically reconstructed retinal photoreceptors and found that cone photoreceptor mitochondria play a substantial role in shaping incoming light. In addition to vision research and ophthalmology, such simulations are broadly applicable to studies of the interaction of electromagnetic radiation with biological tissue. Here, we present our method for discretizing complex 3D models of cellular structures for use in FDTD simulations using MEEP, the MIT Electromagnetic Equation Propagation software, including subpixel smoothing at mesh boundaries. Such models can originate from experimental imaging or be constructed by hand. We also include sample code for use in MEEP. Implementation of this algorithm in new code requires understanding of 3D mathematics and may require several weeks of effort, whereas use of our sample code requires knowledge of MEEP and C++ and may take up to a few hours to prepare a model of interest for 3D FDTD simulation. In all cases, access to a facility supercomputer with parallel processing capabilities is recommended. This protocol offers a practical solution to a significant challenge in the field of computational electrodynamics and paves the way for future advancements in the study of light interaction with biological structures.

Light-specific wavelengths differentially affect the exploration rate, opercular beat, skin color change, opsin transcripts, and the oxi-redox system of the longsnout seahorse Hippocampus reidi

Light is a strong stimulus for the sensory and endocrine systems. The opsins constitute a large family of proteins that can respond to specific light wavelengths. Hippocampus reidi is a near-threatened seahorse that has a diverse color pattern and sexual dimorphism. Over the years, H. reidi's unique characteristics, coupled with its high demand and over-exploitation for the aquarium trade, have raised concerns about its conservation, primarily due to their significant impact on wild populations. Here, we characterized chromatophore types in juvenile and adult H. reidi in captivity, and the effects of specific light wavelengths with the same irradiance (1.20 mW/cm2) on color change, growth, and survival rate. The xanthophores and melanophores were the major components of H. reidi pigmentation with differences in density and distribution between life stages and sexes. In the eye and skin of juveniles, the yellow (585 nm) wavelength induced a substantial increase in melanin levels compared to the individuals kept under white light (WL), blue (442 nm), or red (650 nm) wavelengths. In addition, blue and yellow wavelengths led to a higher juvenile mortality rate in comparison to the other treatments. Adult seahorses showed a rhythmic color change over 24 h, the highest reflectance values were obtained in the light phase, representing a daytime skin lightening for individuals under WL, blue and yellow wavelength, with changes in the acrophase. The yellow wavelength was more effective on juvenile seahorse pigmentation, while the blue wavelength exerted a stronger effect on the regulation of adult physiological color change. Dramatic changes in the opsin mRNA levels were life stage-dependent, which may infer ontogenetic opsin functions throughout seahorses' development. Exposure to specific wavelengths differentially affected the opsins mRNA levels in the skin and eyes of juveniles. In the juveniles, skin transcripts of visual (rh1, rh2, and lws) and non-visual opsins (opn3 and opn4x) were higher in individuals under yellow light. While in the juvenile's eyes, only rh1 and rh2 had increased transcripts influenced by yellow light; the lws and opn3 mRNA levels were higher in juveniles' eyes under WL. Prolonged exposure to yellow wavelength stimulates a robust increase in the antioxidant enzymes sod1 and sod2 mRNA levels. Our findings indicate that changes in the visible light spectrum alter physiological processes at different stages of life in H. reidi and may serve as the basis for a broader discussion about the implications of artificial light for aquatic species in captivity.

Wood-based superblack

Light is a powerful and sustainable resource, but it can be detrimental to the performance and longevity of optical devices. Materials with near-zero light reflectance, i.e. superblack materials, are sought to improve the performance of several light-centered technologies. Here we report a simple top-down strategy, guided by computational methods, to develop robust superblack materials following metal-free wood delignification and carbonization (1500 °C). Subwavelength severed cells evolve under shrinkage stresses, yielding vertically aligned carbon microfiber arrays with a thickness of ~100 µm and light reflectance as low as 0.36% and independent of the incidence angle. The formation of such structures is rationalized based on delignification method, lignin content, carbonization temperature and wood density. Moreover, our measurements indicate a laser beam reflectivity lower than commercial light stoppers in current use. Overall, the wood-based superblack material is introduced as a mechanically robust surrogate for microfabricated carbon nanotube arrays.

The carotenoid redshift: Physical basis and implications for visual signaling

Carotenoid pigments are the basis for much red, orange, and yellow coloration in nature and central to visual signaling. However, as pigment concentration increases, carotenoid signals not only darken and become more saturated but they also redshift; for example, orange pigments can look red at higher concentration. This occurs because light experiences exponential attenuation, and carotenoid-based signals have spectrally asymmetric reflectance in the visible range. Adding pigment disproportionately affects the high-absorbance regions of the reflectance spectra, which redshifts the perceived hue. This carotenoid redshift is substantial and perceivable by animal observers. In addition, beyond pigment concentration, anything that increases the path length of light through pigment causes this redshift (including optical nano- and microstructures). For example, male Ramphocelus tanagers appear redder than females, despite the same population and concentration of carotenoids, due to microstructures that enhance light-pigment interaction. This mechanism of carotenoid redshift has sensory and evolutionary consequences for honest signaling in that structures that redshift carotenoid ornaments may decrease signal honesty. More generally, nearly all colorful signals vary in hue, saturation, and brightness as light-pigment interactions change, due to spectrally asymmetrical reflectance within the visible range of the relevant species. Therefore, the three attributes of color need to be considered together in studies of honest visual signaling.

Mesopelagic fishes of the North-West African Upwelling from the Discovery Collections

Background

Mesopelagic fish specimens from two stations in the NW African Upwelling were identified and catalogued to produce a Darwin Core-aligned dataset. A total of 9655 individual fishes were identified, with 9017 specimens identified at least to genus level and 3124 specimens identified to species level. This dataset comprises specimens collected from the 1990 RRS Discovery (III) Cruise D195 and was used to investigate depth-related trends in diversity and community composition alongside species-specific migratory behaviour. The finalised dataset was published on OBIS through the Deep-Sea node.

New information

This dataset contains occurrence and abundance data for midwater fishes caught between the Mauritanian coast and Cape Verde, published for the first time. The dataset records 146 different fish taxa. Twenty-three taxa in the dataset are not present in any prior OBIS datasets that cover the area. These novel taxa are: Bathylagusandriashevi, Bolinichthysindicus, Bolinichthyssupralateralis, Cyclothoneparapallida, Dolichopteroidesbinocularis, Gigantactis indet. Gymnoscopelus stet., Howellaatlantica, Hygophumproximum, Hygophumtaaningi, Ichthyococcuspolli, Lampadenaanomala, Lampanyctuscuprarius, Lampanyctusisaacsi, Lampanyctuslineatus, Lampanyctusmacdonaldi, Lampanyctusnobilis, Lestidiopsmirabilis, Loweinarara, Macroparalepisbrevis, Melamphaesmicrops and Melanonusgracilis. An anglerfish specimen belonging to Linophrynidae was also found, the first in the leftvent family to be logged in the area on OBIS; however, the specimen was too damaged to identify beyond this level.

Supreme-black levels enabled by touchproof microcavity surface texture on anti-backscatter matrix

Emerging immersive high-dynamic range display technologies require not only high peak luminance but also true black levels with hemispherical reflectance below 0.001 (0.1%) to accommodate the wide dynamic range of the human eye (~10⁵). Such low reflectance materials, denoted here as "supreme black," must exhibit near-perfect surface antireflection, extremely low in-matrix backscattering, and sufficient optical thickness, which, to date, have only been achieved by fragile sparse materials. We demonstrate a record-low hemispherical reflectance below 0.0002 (absorptance above 0.9998) in a touchproof material by satisfying the three requirements with a superwavelength surface microtexture with nanolevel details, low Mie backscattering composition, and optional additional underlayer. Our supreme black finishes are one to two orders of magnitude blacker than previously developed touchproof super-black materials. Thereby, unprecedented black levels enabling an ambient contrast ratio of ≳10⁴ would be provided in display devices, contributing to immersive visual experiences that are critical for seamless remote collaboration and reliable virtual health care.

Hepatopancreas immune response during different photoperiods in the Chinese mitten crab, Eriocheir sinensis

Photoperiod plays an important role in the growth, development, and metabolism of crustaceans. The growth and reproduction of crabs are closely related to the photoperiod. The hepatopancreas is an important source of innate immune molecules; however, hepatopancreatic patterns of gene expression depending on the photoperiod-which may underlie changes in immune mechanisms-remain unknown. To study the molecular basis of immune regulation in the Chinese mitten crab (Eriocheir sinensis) under different light conditions, a new generation of high-throughput Illumina sequencing technology was used, and functional genes associated with immune function in the hepatopancreas of this crab were explored via assembly of high-quality sequences, gene annotation, and classification. A total of 383,899,798 clean reads from the hepatopancreas of the normal group (12 h/12 h L:D), 387,936,676 clean reads from the continuous light group (24 h/0 h L:D), and 384,872,734 clean reads from the continuous darkness group (0 h/24 h L:D) were obtained. Compared with the normal group, 141, 152, 60, 87, 90, and 101 differentially expressed genes were identified in the groups exposed to continuous light for 2 days, continuous darkness for 2 days, continuous light for 4 days, continuous darkness for 4 days, continuous light for 6 days, and continuous darkness for 6 days, respectively. The results of this study revealed that under continuous light and dark conditions, the crabs were most affected by light on day 2, but the interference gradually decreased with time. We suggest that long-term light or dark treatment makes crabs adaptable to fluctuations in the photoperiod. The expression of genes associated with immune response patterns was found to change during different photoperiods. Prophenoloxidase (proPO) and serine proteinase (kazal-type serine proteinase inhibitor 1 and serine proteinase inhibitor-3) in the proPO-activating system were significantly upregulated in the 2-day continuous light group. Glutathione peroxidase 3 was significantly downregulated under continuous light exposure, while cyclooxygenase was upregulated in the continuous light and dark environments. These results provide insights into the molecular mechanism underlying the effects of the photoperiod on immune regulation and the physiological activity of E. sinensis.

Engineering Biomimetic Nanostructured "Melanosome" Textiles for Advanced Solar-to-Thermal Devices

In nature, deep-sea fish featured with close-packed melanosomes can remarkably lower light reflection, which have inspired us to design ultrablack coatings for enhanced solar-to-thermal conversion. Herein, a biomimetic ultrablack textile is developed enabled by the formation of hierarchical polypyrrole (Ppy) nanospheres. The fabricated textile exhibits prominently suppressed reflectance of lower than 4% and highly enhanced absorption of up to 96%. Further experimental results and molecular dynamics (MD) simulation evidence the formation process of hierarchical nanospheres. Based on high-efficient solar-to-thermal conversion, the biomimetic textile with desirable conductivity allows the development of a salt-free solar evaporator, enabling a sustainable seawater evaporation rate of up to 1.54 kg m^-2 h^-1 under 1 sun. Furthermore, the biomimetic hierarchical textile exhibits good superhydrophobicity, enhanced photothermal property, and high electrothermal conversion, demonstrating significant potential in wearable thermal management (rescue vests) in water conditions.

Cell Junction and Vesicle Trafficking-Mediated Melanosome/Melanin Transfer Are Involved in the Dynamic Transformation of Goldfish Carassius auratus Skin Color

Goldfish are one of the most popular models for studying the genetic diversity of skin color. Transcriptome sequencing (RNA-seq) and whole genome bisulfate sequencing (WGBS) of skin tissues from the third filial (F3) cyan (CN), black (BK), and white (WH) goldfish were conducted to analyze the molecular mechanism of color transformation in fish. The RNA-seq yielded 56 Gb of clean data and 56,627 transcripts from nine skin samples. The DEGs (differentially expressed genes) were enriched in cell junction cellular components and the tight junction pathway. Ninety-five homologs of the claudin family were predicted and 16 claudins were identified in correlation with skin color transformation. WGBS yielded 1079 Gb of clean data from 15 samples. Both the DEGs and the DMRs (differentially methylated regions) in the BK_CN group were found to be enriched in cytoskeleton reorganization and vesicle trafficking. Masson staining and TEM (transmission electron microscopy) confirmed the varied distribution and processes of melanosome/melanin in skin tissues. Our results suggested that cytoskeleton reorganization, cell junction, and the vesicle trafficking system played key roles in the transfer of the melanosome/melanin, and it was the extracellular translocation rather than the biosynthesis or metabolism of the melanin process that resulted in the color transformation of cyan goldfish. The data will facilitate the understanding of the molecular mechanisms underlying dynamic skin color transformation in goldfish.

Analysis of pigment cell composition, pigment content, tyrosinase content and activity of three kinds of loaches Misgurnus anguillicaudatus from Poyang Lake

Pigment cell composition, pigment content, tyrosinase content and activity analysis were investigated on three kinds of loaches Misgurnus anguillicaudatus: big blackspot loaches (BBL), small blackspot loaches (SBL) and non-blackspot loaches (NBL), from Poyang Lake. Results showed that there were three types of skin pigment cells, namely melanophores, xanthophores and iridophores. Melanophores in dorsum were more than those in abdomen. Melanophore cytosomes in BBL were larger than those in SBL and NBL, and melanosomes were the largest in stage four. The melanophores in dorsal skin of SBL or NBL were small cell bodies, spindle-like and in chain distribution. There was an extremely significant difference in melanin content in BBL between the dorsum and abdomen (P < 0.01). There were no significant differences in melanin abdominal content, lutein and carotenoid contents among three kinds of loaches (P > 0.05). In dorsal skin, tyrosinase content was the highest in BBL, and it was significantly lower in NBL than in BBL and SBL (P < 0.01). This study reveals the differences in pigment and tyrosinase content in three kinds of loaches and provides a theoretical basis for further study of the mechanism of black spot formation.

Does dietary β-carotene influence ontogenetic colour change in the southern corroboree frog?

Ontogenetic colour change occurs in a diversity of vertebrate taxa and may be closely linked to dietary changes throughout development. In various species, red, orange and yellow colouration can be enhanced by the consumption of carotenoids. However, a paucity of long-term dietary manipulation studies means that little is known of the role of individual carotenoid compounds in ontogenetic colour change. We know even less about the influence of individual compounds at different doses (dose effects). The present study aimed to use a large dietary manipulation experiment to investigate the effect of dietary β-carotene supplementation on colouration in southern corroboree frogs (Pseudophryne corroboree) during early post-metamorphic development. Frogs were reared on four dietary treatments with four β-carotene concentrations (0, 1, 2 and 3 mg g-1), with frog colour measured every 8 weeks for 32 weeks. β-Carotene was not found to influence colouration at any dose. However, colouration was found to become more conspicuous over time, including in the control treatment. Moreover, all frogs expressed colour maximally at a similar point in development. These results imply that, for our study species, (1) β-carotene may contribute little or nothing to colouration, (2) frogs can manufacture their own colour, (3) colour development is a continual process and (4) there may have been selection for synchronised development of colour expression. We discuss the potential adaptive benefit of ontogenetic colour change in P. corroboree. More broadly, we draw attention to the potential for adaptive developmental synchrony in the expression of colouration in aposematic species.

Finite-difference Time-domain (FDTD) Optical Simulations: A Primer for the Life Sciences and Bio-Inspired Engineering

Light influences most ecosystems on earth, from sun-dappled forests to bioluminescent creatures in the ocean deep. Biologists have long studied nano- and micro-scale organismal adaptations to manipulate light using ever-more sophisticated microscopy, spectroscopy, and other analytical equipment. In combination with experimental tools, simulations of light interacting with objects can help researchers determine the impact of observed structures and explore how variations affect optical function. In particular, the finite-difference time-domain (FDTD) method is widely used throughout the nanophotonics community to efficiently simulate light interacting with a variety of materials and optical devices. More recently, FDTD has been used to characterize optical adaptations in nature, such as camouflage in fish and other organisms, colors in sexually-selected birds and spiders, and photosynthetic efficiency in plants. FDTD is also common in bioengineering, as the design of biologically-inspired engineered structures can be guided and optimized through FDTD simulations. Parameter sweeps are a particularly useful application of FDTD, which allows researchers to explore a range of variables and modifications in natural and synthetic systems (e.g., to investigate the optical effects of changing the sizes, shape, or refractive indices of a structure). Here, we review the use of FDTD simulations in biology and present a brief methods primer tailored for life scientists, with a focus on the commercially available software Lumerical FDTD. We give special attention to whether FDTD is the right tool to use, how experimental techniques are used to acquire and import the structures of interest, and how their optical properties such as refractive index and absorption are obtained. This primer is intended to help researchers understand FDTD, implement the method to model optical effects, and learn about the benefits and limitations of this tool. Altogether, FDTD is well-suited to (i) characterize optical adaptations and (ii) provide mechanistic explanations; by doing so, it helps (iii) make conclusions about evolutionary theory and (iv) inspire new technologies based on natural structures.

Enhanced photothermal absorption in iridescent feathers

The diverse colours of bird feathers are produced by both pigments and nanostructures, and can have substantial thermal consequences. This is because reflectance, transmittance and absorption of differently coloured tissues affect the heat loads acquired from solar radiation. Using reflectance measurements and heating experiments on sunbird museum specimens, we tested the hypothesis that colour and their colour producing mechanisms affect feather surface heating and the heat transferred to skin level. As predicted, we found that surface temperatures were strongly correlated with plumage reflectivity when exposed to a radiative heat source and, likewise, temperatures reached at skin level decreased with increasing reflectivity. Indeed, nanostructured melanin-based iridescent feathers (green, purple, blue) reflected less light and heated more than unstructured melanin-based colours (grey, brown, black), as well as olives, carotenoid-based colours (yellow, orange, red) and non-pigmented whites. We used optical and heat modelling to test if differences in nanostructuring of melanin, or the bulk melanin content itself, better explains the differences between melanin-based feathers. These models showed that the greater melanin content and, to a lesser extent, the shape of the melanosomes explain the greater photothermal absorption in iridescent feathers. Our results suggest that iridescence can increase heat loads, and potentially alter birds' thermal balance.

Morphological convergence and adaptation in cave and pelagic scale worms (Polynoidae, Annelida)

Across Annelida, accessing the water column drives morphological and lifestyle modifications-yet in the primarily "benthic" scale worms, the ecological significance of swimming has largely been ignored. We investigated genetic, morphological and behavioural adaptations associated with swimming across Polynoidae, using mitogenomics and comparative methods. Mitochondrial genomes from cave and pelagic polynoids were highly similar, with non-significant rearrangements only present in cave Gesiella. Gene orders of the new mitogenomes were highly similar to shallow water species, suggestive of an underlying polynoid ground pattern. Being the first phylogenetic analyses to include the holopelagic Drieschia, we recovered this species nested among shallow water terminals, suggesting a shallow water ancestry. Based on these results, our phylogenetic reconstructions showed that swimming evolved independently three times in Polynoidae, involving convergent adaptations in morphology and motility patterns across the deep sea (Branchipolynoe), midwater (Drieschia) and anchialine caves (Pelagomacellicephala and Gesiella). Phylogenetic generalized least-squares (PGLS) analyses showed that holopelagic and anchialine cave species exhibit hypertrophy of the dorsal cirri, yet, these morphological modifications are achieved along different evolutionary pathways, i.e., elongation of the cirrophore versus style. Together, these findings suggest that a water column lifestyle elicits similar morphological adaptations, favouring bodies designed for drifting and sensing.

Melanin-Inspired Chromophoric Microparticles Composed of Polymeric Peptide Pigments

Melanin and related polyphenolic pigments are versatile functional polymers that serve diverse aesthetic and protective roles across the living world. These polymeric pigments continue to inspire the development of adhesive, photonic, electronic and radiation-protective materials and coatings. The properties of these structures are dictated by covalent and non-covalent interactions in ways that, despite progress, are not fully understood. It remains a major challenge to direct oxidative polymerization of their precursors (amino acids, (poly-)phenols, thiols) toward specific structures. By taking advantage of supramolecular pre-organization of tyrosine-tripeptides and reactive sequestering of selected amino acids during enzymatic oxidation, we demonstrate the spontaneous formation of distinct new chromophores with optical properties that are far beyond the range of those found in biological melanins, in terms of color, UV absorbance and fluorescent emission.

Evolution of pigment cells and patterns: recent insights from teleost fishes

Skin pigment patterns of vertebrates are stunningly diverse, and nowhere more so than in teleost fishes. Several species, including relatives of zebrafish, recently evolved cichlid fishes of East Africa, clownfishes, deep sea fishes, and others are providing insights into pigment pattern evolution. This overview describes recent advances in understanding periodic patterns, like stripes and spots, the loss of patterns, and the role of cell-type diversification in generating pigmentation phenotypes. Advances in this area are being facilitated by the application of modern methods of gene editing, genomics, computational analysis, and other approaches to non-traditional model organisms having interesting pigmentary phenotypes. Several topics worthy of future attention are outlined as well.

Towards an ecology of protective coloration

The strategies underlying different forms of protective coloration are well understood but little attention has been paid to the ecological, life-history and behavioural circumstances under which they evolve. While some comparative studies have investigated the ecological correlates of aposematism, and background matching, the latter particularly in mammals, few have examined the ecological correlates of other types of protective coloration. Here, we first outline which types of defensive coloration strategies may be exhibited by the same individual; concluding that many protective coloration mechanisms can be employed simultaneously, particularly in conjunction with background matching. Second, we review the ecological predictions that have been made for each sort of protective coloration mechanism before systematically surveying phylogenetically controlled comparative studies linking ecological and social variables to antipredator defences that involve coloration. We find that some a priori predictions based on small-scale empirical studies and logical arguments are indeed supported by comparative data, especially in relation to how illumination affects both background matching and self-shadow concealment through countershading; how body size is associated with countershading, motion dazzle, flash coloration and aposematism, although only in selected taxa; how immobility may promote background matching in ambush predators; and how mobility may facilitate motion dazzle. Examination of nearly 120 comparative tests reveals that many focus on ecological variables that have little to do with predictions derived from antipredator defence theory, and that broad-scale ecological studies of defence strategies that incorporate phylogenetics are still very much in their infancy. We close by making recommendations for future evolutionary ecological research.